1. Field of Invention
The present invention relates to valve seats. More particularly, the present invention relates to a sintered alloy for valve seats in which MnS is added for improving machinability and tempering, and a manufacturing method valve seat using the same.
2. Description of Related Art
A valve seat of engine components for vehicles is a component that contacts a valve surface and maintains an airtight seal in a combustion chamber. The valve seat is repeatedly impacted so it needs to be manufactured so it cannot be damaged by the repeated impacts.
A traditional wear-resistant sintered alloy for a valve seat has iron (Fe) as its main component, and contains carbon (C) at 0.4-1.0 wt %, silicon (Si) at 0.1-1.0 wt %, chromium (Cr) at 0.5-2.0 wt %, molybdenum (Mo) at 6.0-10.0 wt %, cobalt (Co) at 6.0-15.0 wt %, and lead (Pb) at 6.0-18.0 wt %. The manufacturing process thereof is as follows.
Firstly, a metal powder except lead of the components is mixed, and it is formed by surface pressure of 4-8 ton/cm2.
It is pre-sintered in the range of 750-800° C. for 40 minutes in a reduction atmosphere, and forged by surface pressure of 7-10 ton/cm2.
Main sintering is then performed in a hydrogen atmosphere in the range of 1110-1140° C. for 30-50 minutes, a resin is impregnated to improve workability, and a barrel process is performed to manufacture a wear-resistant sintered alloy for valve seat.
However, the sintered alloy for the valve seat manufactured by the components and content induces excessive abrasion of tools and tearing, and the workability is not good. Therefore, improvement is needed.
The information disclosed in this Background section is only for enhancement of understanding of the general background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art.